Generally, a substrate processing apparatus includes a chamber for accommodating a wafer serving as a substrate. The substrate processing apparatus performs a plasma process on the wafer by using plasma generated from a processing gas in a processing space in the chamber. The processing gas is supplied into the processing space in the chamber through a shower head disposed at an upper portion of the chamber.
FIGS. 10A and 10B schematically show a configuration of a shower head in a conventional substrate processing apparatus. FIG. 10A illustrates a cross sectional view of a conventional shower head. FIG. 10B illustrates a bottom view of the conventional shower head. Further, FIG. 10A illustrates a cross sectional view taken along a line 10A-10A of FIG. 10B.
As shown in FIGS. 10A and 10B, a shower head 90 includes a circular plate-shaped shower plate 91, a circular plate-shaped cooling plate 92 disposed on the shower plate 91 and a plate supporting body 93 for supporting the shower plate 91. The plate supporting body 93 is formed of a cylindrical member having a portion bored from the bottom. The shower plate 91 and the cooling plate 92 are received in the bored portion. The cooling plate 92 and the plate supporting body 93 form a space 94 between the cooling plate 92 and the plate supporting body 93. A processing gas is introduced into the space 94 from a processing gas inlet pipe 95. Further, the shower plate 91 faces a processing space (not shown) in the chamber.
The shower plate 91 and the cooling plate 92 have a plurality of gas holes 96 and 97 formed therethrough in their thickness directions, respectively. The space 94 communicates with the processing space via the gas holes 96 and 97. The processing gas introduced into the space 94 is supplied into the processing space through the gas holes 96 and 97. Further, since the gas holes 96 are arranged dispersedly as shown in FIG. 10B, the processing gas is also supplied dispersedly.
However, as known conventionally, plasma in the processing space flows into the gas holes 96 and 97 to cause abnormal discharge in the gas holes 96 and 97. When abnormal discharge occurs, alumite is peeled off from the cooling plate 92 to generate particles.
Accordingly, the gas holes of the shower plate or the cooling plate are formed in a labyrinthine shape to prevent plasma from flowing into the gas holes, thereby preventing abnormal discharge in the gas holes (see, for example, Japanese Laid-open Publication No. 2007-5491 and U.S. Patent Application Publication No. 2006/0288934 A1).
However, even though the gas holes are formed in a labyrinthine shape, when the shower plate is used for a while, abnormal discharge occurs in the gas holes.
In the shower plate 91 having the gas holes 96 in which abnormal discharge occurs, part of the gas holes 96 near to the processing space are expanded in a balloon shape as shown in FIG. 11. Accordingly, local discharge is generated in the gas holes 96, and the gas holes 96 are gradually eroded by the local discharge. If an expanded level of the gas holes 96 exceeds a certain value, it is assumed that abnormal discharge can occur therein.